Quote:
Originally Posted by skenn_ie
Bigger ones, even if you can hear them, aren't as irritating. DO check the turbine static balance before fitting though. Fit a switch to force the braking load if it is getting on your nerves.
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Kiss Balancing
Wind generator noises aren't entirely the fault of blade design. Sometimes it's also a matter of balance.
I have one of the large-fan versions, a KISS, with which we are well pleased, despite its having been very abused in our 14 years of use (which included a 12-hour
salt water immersion and an extended fresh
water immersion, both of which responded to a spraydown with fresh
water, an air-dry, and spray with
Corrosion Block before reassembly).
However, a balancing axle is available. A static balance may match by weight, but does not include rotational forces. If you have a different model
wind generator, you may have to fabricate a balancing axle; it will be well worth the effort.
KISS is no longer made, but new blades and hub are available from the prior manufacturer (now retired). The blades are gram-matched, ostensibly meaning that when you mount them, all is good.
Not so fast, Bucko. Dynamic balance that rig!
I used lead tape. In order to balance (see below on my modus), it took over a foot on two of the blades. It has to be done in a windless - not a breath of air -
environment, of course. And, natch, I attach at the back side of the blade so as to not muck with the aerodynamics.
Here's how I measure whether I'm truly balanced or not:
My not-perfectly straight-flat workbench in the walkthrough has a fiddle. I find a level spot (how full the
tanks are, and
davits, and so on affects that) for one end of the axle, and use an
aluminum torpedo level for the other. If both ends are level, it should not rotate if it's balanced. When it IS balanced, a slight tilt of the level (max bubble-touch, not way off) will cause the blade to rotate with the axle heading downhill. As my axle ends are about 1/4 inch, you can imagine that it takes a fair amount of torque to move a 30" blade - but, while slow, it WILL rotate, but not do so when level.
So, start by determining the heavy blade. That's the one which will end up "down" (probably not straight down unless the other two blades happen to be exactly matched). You'll be lead-taping the "light" blades. The previously "heavy" blade will become the "light" blade.
I put on the tape in amounts I estimate will
work (it comes with a plastic sheet backing, like you'd find on double-stick tape rolls), sticking the ends lightly, initially. I start with one end relatively close to the hub. Some fiddling with how far out the tape is, and I'm close. When I have it reasonably close, with tape on two of the three blades, I get down to fine tuning.
By "close" I mean that the blades will rotate, but only slowly, with the bare blade (now) light. By that I mean that regardless of whether I start the blade at 8 or 4 in clock position, it wants to rise to the top from there. I then remove all the protective tape and fully attach the lead.
I then start, with a utility knife, removing segments of the tape from the ends to balance (slice gently so as to not damage the blade). Keep your pieces; you likely will have to fiddle with matching up the two weighted blades; mine are as small, as I get close, as 1/8" - but if handled carefully, will re-adhere. I start relatively large and get smaller as I approach nirvana
In the end, my metric is that the unweighted (now "heavy") blade, from either 10 or 2 clock positions, takes a minute or more to reach bottom - and that I can make the smallest adjustment to 'level' and also have it turn.
The difference, at least in our KISS, is stark. A mere Whiiiiissssshhhh, instead of a moan or groan or roar.
I suspect that any blade set could be similarly balanced, whether KISS or not. If you can put your hand on however it's mounted, and can feel vibration in the pole, likely your blades are not really balanced, even if your blade weights are within micrograms of each other...
L8R
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